Low-vigor seeds of black-eyed Susan (Rudbeckia fulgida Ait.) primed in aerated -1.3 MPa KNO3 for 7 days at 30C in darkness had double the total germination percentage at 30C and one-half the mean time of germination as nonprimed seeds. Priming the seeds in polyethylene glycol rather than KNO3 generally resulted in lower total germination percentage and longer mean time of germination. Osmotic priming increased total germination percentage and germination rate of seeds germinated at 21.9 to 32.2C, but the priming benefit on total germination percentage was greater at ≤27.6C. Total germination percentage of primed and nonprimed seeds was highest at 28.8 to 32.2C.